We have previously shown adenosine 3', 5'-monophosphate (cAMP) and its dibutyryl analog to promote microtubule-dependent, in vitro, neurite maturation. To determine if the enhanced development is accompanied by increased protein and ribonucleic acid (RNA) synthesis, the relative rates of total protein and RNA synthesis in the presence and absence of dibutyryl-cAMP were measured. At time periods where a pronounced stimulation of neurite maturation was observed in the presence of the nucleotide, the incorporation of C14-uridine and H3-amino acids into acid precipitable material was unchanged relative to controls. The return of sensorimotor function following a crush lesion of rat sciatic nerves has been studied in the presence or absence of dibutyryl cAMP. Animals exposed to daily injections of the nucleotide showed a significant increase in the return of sensorimotor function. Ultrastructural studies reveal greater numbers of myelinated fibers in comparable perivascular regions of 8 day distal nerve fragments treated with dibutyryl cAMP than saline controls. The role of microfilaments (cytochalasin B) and microtubules (colcemid) in axoplasmic transport of incorporated amino acids has been studied by autoradiography. The presence of 10 microns/ml of cytochalasin B in the culture medium did not significantly affect the distribution of label along sensory neurites. Nerve processes exposed to concentrations of colcemid sufficient to cause neurite retraction (0.2 microns/ml) did not have a reduced distribution of labeling. These data suggest that microtubules play a more active role in axoplasmic transport than microfilaments. BIBLIOGRAPHIC REFERENCES: Murphy, Richard, W. Stirewalt and F. Roisen, 1976. A comparison of the effects of dibutyrylcyclic AMP on macromolecular synthesis and maturation of chick sensory ganglia in vitro. Proc. Soc. Exp. Biol. and Med. (in press). Roisen, Fred J. 1975. The effects of dimethyl sulfoxide on neurite development. "In Vitro". Ann. N.Y. Acad. Sci. "243": 279-296.